Phosphorylation of Mouse Immunity-Related GTPase (IRG) Resistance Proteins Is an Evasion Strategy for Virulent Toxoplasma gondii

GTPases of the mouse IRG protein family, mediators of resistance against Toxoplasma gondii in the mouse, are inactivated by a polymorphic kinase of the parasite, resulting in enhanced parasite virulence

Comparative Genomics of the Apicomplexan Parasites Toxoplasma gondii and Neospora caninum: Coccidia Differing in Host Range and Transmission Strategy

Toxoplasma gondii is a zoonotic protozoan parasite which infects nearly one third of the human population and is found in an extraordinary range of vertebrate hosts. Its epidemiology depends heavily on horizontal transmission, especially between rodents and its definitive host, the cat. Neospora caninum is a recently discovered close relative of Toxoplasma, whose definitive host is the dog. Both species are tissue-dwelling Coccidia and members of the phylum Apicomplexa; they share many common features, but Neospora neither infects humans nor shares the same wide host range as Toxoplasma, rather it shows a striking preference for highly efficient vertical transmission in cattle. These species therefore provide a remarkable opportunity to investigate mechanisms of host restriction, transmission strategies, virulence and zoonotic potential. We sequenced the genome of N. caninum and transcriptomes of the invasive stage of both species, undertaking an extensive comparative genomics and transcriptomics analysis. We estimate that these organisms diverged from their common ancestor around 28 million years ago and find that both genomes and gene expression are remarkably conserved. However, in N. caninum we identified an unexpected expansion of surface antigen gene families and the divergence of secreted virulence factors, including rhoptry kinases. Specifically we show that the rhoptry kinase ROP18 is pseudogenised in N. caninum and that, as a possible consequence, Neospora is unable to phosphorylate host immunity-related GTPases, as Toxoplasma does. This defense strategy is thought to be key to virulence in Toxoplasma. We conclude that the ecological niches occupied by these species are influenced by a relatively small number of gene products which operate at the host-parasite interface and that the dominance of vertical transmission in N. caninum may be associated with the evolution of reduced virulence in this species

Rep and Rep′ Protein of Porcine circovirus Type 1 Bind to the Origin of Replication in Vitro

AbstractGenome replication of Porcine circovirus type 1 (PCV1) relies upon expression of the full-length protein Rep and a spliced isoform (Rep′), and the presence of a 111-bp genomic fragment comprising the origin of replication. Using an electrophoretic mobility shift assay (EMSA), the capability of both Rep proteins to bind to partial fragments of the origin of replication of PCV1 was investigated in vitro. Both proteins formed complexes with double-stranded DNA origin fragments containing a stem-loop structure with a conserved nonamer and four hexamer repeats (5′-CGGCAG; H1 to H4). Use of truncated EMSA substrates identified minimal binding sites (MBS) for Rep and Rep′ protein: The Rep binding site was mapped to the right leg of the stem-loop and the two inner hexamer repeats H1/H2, while binding of Rep′ required only the presence of two hexamer repeats. Two differentially retarded complexes were observed with Rep protein, which presumably result from alternative binding to the MBS or to H3/4

Functional Analysis of cis- and trans-Acting Replication Factors of Porcine Circovirus Type 1▿

The replication proteins Rep and Rep′ of porcine circovirus type 1 (PCV1) are both capable of introducing and resealing strand discontinuities at the viral origin of DNA replication in vitro underlying genome amplification by rolling-circle replication. The PCV1 origin of replication encompasses the minimal binding site (MBS) of the Rep and Rep′ proteins and an inverted repeat with the potential to form a stem-loop. In this study, both elements of the PCV1 origin were demonstrated to be essential for viral replication in transfected cells. Furthermore, investigation of conserved amino acid motifs within Rep and Rep′ proteins revealed that the mutation of motifs I, II, and III and of the GKS box interfered with viral replication. In vitro studies demonstrated that motifs I to III were essential for origin cleavage, while the GKS box was dispensable for the initiation of viral replication. A covalent link between Rep/Rep′ and the DNA after origin cleavage was demonstrated, providing a mechanism for energy conservation for the termination of replication

New Reporter Gene-Based Replication Assay Reveals Exchangeability of Replication Factors of Porcine Circovirus Types 1 and 2

Two types of porcine circovirus (PCV), which differ in their pathogenicity, are known. PCV type 2 (PCV2) is the etiological agent of postweaning multisystemic wasting syndrome in swine, while PCV1 has not yet been linked to a disease. Corroborating earlier observations in PCV1, transcript mapping revealed that the rep gene of PCV2 encodes two products, the full-length protein Rep and the spliced version Rep′ and that the simultaneous expression of Rep and Rep′ proteins is essential for initiation of replication of PCV2. The interchangeability of the replication factors of PCV1 and PCV2 was examined. The rep gene products of PCV2 were not only able to bind the PCV2 origin but also the origin of PCV1 and vice versa. To investigate the competence of the Rep/Rep′ proteins to initiate replication at the heterologous origin, a new replication assay was developed. It measures the expression of a luc reporter gene present on a plasmid carrying the origin of the investigated replicon. Replication is initiated by expression of the appendant replicase from a second plasmid and results in replication of the origin plasmid coupled with an increase in the Luc activity. Using this method to compare replication of PCV1 and PCV2 in cell culture, it was shown that the Rep/Rep′ protein of PCV2 initiated replication at the origin of PCV1, as did the reciprocal combination. Our results indicate that the cis- and trans-acting replication factors of the two viruses are functionally exchangeable

Intraoperative management of combined general anesthesia and thoracic epidural analgesia: A survey among German anesthetists

Background Evidence concerning combined general anesthesia (GA) and thoracic epidural analgesia (EA) is controversial and the procedure appears heterogeneous in clinical implementation. We aimed to gain an overview of different approaches and to unveil a suspected heterogeneity concerning the intraoperative management of combined GA and EA. Methods This was an anonymous survey among Members of the Scientific working group for regional anesthesia within the German Society of Anaesthesiology and Intensive Care Medicine (DGAI) conducted from February 2020 to August 2020. Results The response rate was 38%. The majority of participants were experienced anesthetists with high expertise for the specific regimen of combined GA and EA. Most participants establish EA in the sitting position (94%), prefer early epidural initiation (prior to skin incision: 80%; intraoperative: 14%) and administer ropivacaine (89%) in rather low concentrations (0.2%: 45%; 0.375%: 30%; 0.75%: 15%) mostly with an opioid (84%) in a bolus-based mode (95%). The majority reduce systemic opioid doses intraoperatively if EA works sufficiently (minimal systemic opioids: 58%; analgesia exclusively via EA: 34%). About 85% manage intraoperative EA insufficiency with systemic opioids, 52% try to escalate EA, and only 25% use non-opioids, e.g. intravenous ketamine or lidocaine. Conclusions Although, consensus seems to be present for several aspects (patient's position during epidural puncture, main epidural substance, application mode), there is considerable heterogeneity regarding systemic opioids, rescue strategies for insufficient EA, and hemodynamic management, which might explain inconsistent results of previous trials and meta-analyses

The Toxoplasma gondii rhoptry protein ROP18 is an Irga6-specific kinase and regulated by the dense granule protein GRA7

In mice, avirulent strains (e. g. types II and III) of the protozoan parasite Toxoplasma gondii are restricted by the immunity-related GTPase (IRG) resistance system. Loading of IRG proteins onto the parasitophorous vacuolar membrane (PVM) is required for vacuolar rupture resulting in parasite clearance. In virulent strain (e. g. type I) infections, polymorphic effector proteins ROP5 and ROP18 cooperate to phosphorylate and thereby inactivate mouse IRG proteins to preserve PVM integrity. In this study, we confirmed the dense granule protein GRA7 as an additional component of the ROP5/ROP18 kinase complex and identified GRA7 association with the PVM by direct binding to ROP5. The absence of GRA7 results in reduced phosphorylation of Irga6 correlated with increased vacuolar IRG protein amounts and attenuated virulence. Earlier work identified additional IRG proteins as targets of T. gondii ROP18 kinase. We show that the only specific target of ROP18 among IRG proteins is in fact Irga6. Similarly, we demonstrate that GRA7 is strictly an Irga6-specific virulence effector. This identifies T. gondii GRA7 as a regulator for ROP18-specific inactivation of Irga6. The structural diversity of the IRG proteins implies that certain family members constitute additional specific targets for other yet unknown T. gondii virulence effectors